The invention has an object of facilitating the detection of defective welds and improving the efficiency of manufacturing electrolyzer units. A a method of manufacturing an electrolyzer unit comprises a step of arranging a partition member on a front surface of a cathode pan and welding a top side and a left side of the cathode pan to the partition member to form a gas-liquid separation chamber, a step of performing a similar step on an anode pan, a step of arranging cathode ribs on a front surface of the cathode pan and clad plates on a back surface of the cathode pan at positions corresponding to the cathode ribs, welding them at the same time, putting a back surface of the anode pan over the back surface of the cathode pan and arranging anode ribs on a front surface of the anode pan at positions corresponding to the clad plates, a step of simultaneously performing on the anode pan a similar step of arranging anode ribs on a front surface of the anode pan at positions corresponding to the clad plates, and a step of inserting frame members into spaces formed between flange portions of the cathode pan and flange portions of the anode pan.